Insulating glass units (IGUs) are used in windows to reduce heat loss from building interiors during cold weather. IGUs are typically formed by a spacer assembly sandwiched between glass lights. A spacer assembly usually comprises a frame structure extending peripherally about the unit, a sealant material adhered both to the glass lights and the frame structure, and a desiccant for absorbing atmospheric moisture within the unit. The margins of the glass lights are flush with or extend slightly outwardly from the spacer assembly. The sealant extends continuously about the frame structure periphery and its opposite sides so that the space within the IGU is hermetic.
There have been numerous proposals for constructing IGUs. One type of IGU was constructed from an elongated body of hot melt material having a corrugated sheet metal strip embedded in it. Desiccant was also embedded in the hot melt. The resulting composite frame forming strip was bent into a rectangular shape and sandwiched between conforming glass lights.
Perhaps the most successful IGU construction has employed tubular, roll formed aluminum or steel frame elements connected at their ends to form a square or rectangular spacer frame. Particulate desiccant deposited inside the tubular frame elements communicated with air trapped in the IGU interior to remove the entrapped airborne water vapor and thus preclude its condensation within the unit. The frame sides and corners were covered with sealant formed by a hot melt material for securing the frame to the glass lights. The sealant provided a barrier between atmospheric air and the IGU interior which blocked entry of atmospheric water vapor. Thus after the water vapor entrapped in the IGU was removed internal condensation only occurred when the unit failed.
Among other reasons, units failed because atmospheric water vapor infiltrated the sealant barrier. Infiltration tended to occur at the frame corners because the opposite frame sides were at least partly discontinuous there. For example, in some frames the corners were formed by cutting "V" shaped notches at corner locations in a single long tube. The notches enabled bending the tube to form mitred corner joints. After bending to form the corners potential infiltration paths extended along the corner parting lines substantially across the opposite frame faces at each corner.
In other frame constructions "corner keys" were inserted between adjacent frame element ends to form the corners. These corner keys produced potential infiltration paths at their junctures with the frame elements. In some constructions the corner keys were foldable so that the sealant could be extruded onto the frame sides as the frame moved linearly past a sealant extrusion station. The frame was then folded to a rectangular configuration with the sealant in place on the opposite sides. In some of these proposals the sealant was extruded into the space between the frame element end edges. When the frame was folded into its final form the sealant extruded between the element ends was not present at the frame corners. This reduction in the amount of sealant at the corners tended to cause vapor leakage paths into the IGU, particularly after the unit was in service over a period of time.
In all these proposals the frame elements were cut to length and, in the case of frames connected together by corner keys, the keys were installed before applying the sealant. These were manual operations. Accordingly, fabricating IGUs from these frames entailed generating scrap and inefficient manual operations.
Still other proposals for spacer frame constructions involved roll forming the spacer elements, sawing a V-shaped notch at each corner location so that the spacer members remained attached and foldable at the corner, filling frame members with desiccant and plugging them and then cutting off the frame member. The frame member was then coated with hot melt and folded onto its final configuration. The sawing, filling and plugging operations had to be performed by hand which slowed production of these frames.
It is known that heat losses from IGUs occur via conductive heat transfer at the edges of the units where the glass lights are attached. The extent of such losses depends upon the conductivity and geometry of the heat path between the lights. Roll formed spacer frames were tubular so that two frame element walls extended between the glass lights. The heat path extended from the warmer light through the sealant coating the adjacent frame side, both frame element walls extending between the lights, and through the sealant on the opposite frame side to the cooler light.
The sealant materials presented a heat flow path having a large cross sectional area and the hot melt materials themselves were not highly effective insulators. Accordingly the heat path through the sealants was capable of substantial heat conduction. The limiting factor in the heat path was the spacer frame walls. They had relatively small cross sectional areas which tended to restrict heat flow. However, frame element conductivity was great particularly because aluminum, the typical frame material, is highly conductive. Thus the heat losses due to conduction along the edges of the IGUs were significant.
Moreover, because the heat losses occurred along concentric paths spaced inwardly from the glass light peripheries, the warmer glass lights tended to be "cold" well inwardly from their peripheries. Beside the disadvantage of heat loss, cold edge IGUs caused other unacceptable problems. For example, condensation tended to occur on the margins of the warmer glass light. This was unsightly and the accumulated moisture was particularly destructive to wooden IGU support structures, such as wooden window frames. Furthermore, condensed moisture could freeze along the margins of the indoor light during cold weather. This threatened damage to the IGU support structure.
The present invention provides a new and improved IGU and method of making it wherein completed IGUs exhibit significantly reduced "cold edge" effects and spacer frame assembly construction is conducted at high production rates, creating little scrap and involving minimal handling. The new IGU is structurally strong and durable, functionally superior to the prior units and can be produced in a highly efficient manner.